1. Field of the Invention
The present invention relates to an endoscope system, an endoscope video processor and a method of driving the endoscope system for internal examination using normal light and special light, such as white light and infrared light.
2. Description of Related Art
Endoscopic examination is widely used in a medical field. A typical electronic endoscope has a CCD image sensor, or a similar imaging device, at a distal end of an insertion section to be inserted into the body of a patient. The electronic endoscope is connected to an endoscope video processor and a light source device by means of a cable and connectors.
The endoscope video processor applies various types of processing to an image signal of the imaging device, and produces an internal body image, which is displayed on a monitor for medical diagnosis. The light source device has a white light source, such as a xenon lamp, and provides illumination light to the electronic endoscope.
In the medical endoscopic examination, an imaging technique called NBI (Narrow Bandwidth Imaging) is used to facilitate the detection of disease. In the NBI, a diseased site is illuminated by narrow bandwidth light (hereinafter, special illumination light), instead by spectrally broad white light (hereinafter, normal illumination light), and its reflected light is imaged (the resultant image is hereinafter referred to as a special image, in distinction from a normal image produced with the normal illumination light). This NBI technique allows for obtaining images that highlight submucosal blood vessels or that highlight stomach wall, intestine tissue or other internal organs.
In some cases, a filter turret that combines sectors for normal illumination light and special illumination light is introduced across an illumination light path. This filter turret is moved mechanically by a motor or the like upon a switching operation from a doctor (operator) to obtain the normal image and the special image at substantially the same time.
Also, Japanese Patent Laid-open Publication No. 2007-202589 discloses an electronic endoscope apparatus configured to rotate a filter turret at predetermined time intervals (for example, one filed interval) to place a wide-bandwidth sector (for normal illumination light) and a narrow-bandwidth sector (for special illumination light) interchangeably in the illumination light path. The wide-bandwidth (or normal) image and the narrow-bandwidth (or special) image thus obtained are processed in a wide-bandwidth image processing circuit and a narrow-bandwidth image processing circuit respectively. As a result, the normal and special images can be displayed at substantially the same time (one field difference), and compared with each other in diagnosis.
The above electronic endoscope apparatus needs to have separate image processing circuits because the normal and special images require different types of image processing. Unfortunately, however, two image processing circuits in a single processor results in increasing the component cost and power consumption. Additionally, the size of the apparatus is increased.
In view of this, U.S. Pat. No. 7,479,990 B2 (corresponding to Japanese Patent Laid-open Publication No. 2005-013611) discloses a processor having an FPGA (Field Programmable Gate Array), as an image processing circuit, which can change the circuit configuration programmably in accordance with circuit data. The circuit information for normal images is loaded to the FPGA when the normal images are going to be obtained, and the circuit information for special images is loaded to the FPGA when the special images are going to be obtained. This allows the normal and special images to be processed with this single FPGA. Now, the processor only needs a single processing circuit (or FPGA) for image processing, and is thus able to offer small sizing and low cost.
Additionally, as being configured to execute the wide-bandwidth image processing and the narrow-bandwidth image processing alternately, the FPGA enables to display the normal and special images side by side. The FPGA, however, takes long time to reconfigure the circuit arrangement, and it is difficult to switch between the normal image processing and the special image processing at a substantially short interval, such as one filed or one frame.
Even worse, the FPGA is not able to execute the image processing during the load of the circuit data. The above-mentioned processor is therefore equipped with a bypass circuit for processing the image signals to display monochrome images on the monitor while the FPGA is loading the circuit data. Because of this FPGA problem of unable to provide different types of images at one-filed or one-frame intervals, the FPGA cannot accomplish so-called simultaneous observation for visualizing the normal and special images simultaneously.